1. Field of the Invention
This invention relates to a hydraulic suspension control device for a vehicle, and more particularly to an improved hydraulic suspension control device in which instability yawing of vehicle movement is prevented during vehicle turning maneuvers.
2. Description of the Related Art
A prior hydraulic suspension control device is known from Japanese Laid-Open Print No. 62-198511. Therein, the hydraulic suspension control device provides for obtaining a quick and stable vehicle turning movement by means of an independently controlled rolling stiffness between front and rear wheels. Rolling stiffness is provided in such manner that the steering characteristic of the vehicle can be either over-steering or under-steering in accordance with vehicle behavior during the vehicle turning movement or maneuver.
However, the hydraulic suspension control device is controlled so as to change the steering characteristic of the vehicle into an over-steer characteristic in a first stage of the vehicle turning movement. Therefore, the vehicle rear wheels begin to slip which results in an extremely unstable vehicle behavior.
Another prior hydraulic suspension control device is known from Japanese Laid-Open Print No. 62-275814. Therein, the hydraulic suspension control device is provided to obtain a quick vehicle turning movement by changing into a positive over-steering characteristic according to lateral acceleration and driving force during the vehicle turning movement.
Also, as driving force transmitted to the driving wheels is reduced to zero during braking operation, control of spin or drift during turning movement of the vehicle by use of the brakes is not precisely performed. In addition, since road conditions have not been considered, if a setting of the control is made with the assumption of a relatively high .mu.-road (high coefficient of friction), the vehicle is prone to movement into tail-slide conditions upon generation of high centrifugal force or high driving force. Accordingly, vehicles provided with the foregoing control cannot have an over-steer characteristic since centrifugal force or driving force should be low due to slipping of the vehicle on low .mu.-road (low coefficient of friction).